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Full text of "Text Book Of Mechanical Engineering"

Steam Cylinder in Loam.                        23

they now enable us to remove this outer portion in separate pieces-
to a safe place to dry, and allow us also to build up the internal
core. Thus plate K may be lifted by crane, removing the upper
portion first; next j and d. Discarding the loam plate f, which
is no longer needed, our next proceeding is to take the board N,
Fig. 28, having built up the core loosely with bricks, vented at the
joints with coke powder, and strike out loam to represent the in-
ternal surface of the cylinder j this is dried in place by open fires
and blackwashed. The projecting portions only now remain,,
which, as we have said, must be made from core boxes. Fig. 30
represents the box for the outer contour of the steam ports, and a
core is formed by laying it on a flat plate and filling up with loam.
The parts a a, of the core box should be noticed : sides b b, can
be easily taken away, but in order to draw away the centre c, the
flanges must be dovetailed to c in such a manner that they may
be left behind on withdrawal of the box.

This may be understood on reference to a, which shews one
of these loose pieces. They may afterwards be taken away in the
direction of the arrows. The box and core for the steam ports-
are shown in Fig. 31, and need no explanation.

The inside core for exhaust port, being circular, is struck out .
on a separate plate by board (Fig. 32), box p being required to
give the projection on the steam side, and Q for that on the
exhaust side. There is left the exhaust flange, which may be
formed from the box in Fig. 33, the flange itself being loose on
the pattern to enable the core to be withdrawn, the latter being
made on a plate similarly to Fig. 30.

s s are patterns for the web at top and bottom of the cylinder,
which, having been built into the core at Fig. 270:, may now be
removed.

Finally, all may be put together to form the mould, in the
manner drawn in Fig. 34, beginning at the bottom and putting
the different cores in their places as we proceed; chaplets being
required to support the annular exhaust core. Gates are next
made, which had better enter the mould somewhat low down, in
order to have some head of metal at that point. The object of
this is to prevent air bubbles in the casting, by means of the
weight of in-pouring metal, whatever air there may be in the